Image sensors of the type used in the present invention are called line sensors and are constructed from a multitude of light-sensitive pixels that are arranged along a line. The individual pixels convert input light signals into electrical signals and therefore permit an electronic evaluation of the image information recorded by operation of the image sensor. Such line sensors are employed, for example for inspecting printed products, and in particular are used for inspecting security documents.
The number of pixels required in the line sensor is substantially a function of the width of the object to be recorded and of the resolution required for the line sensor's application in connection with the object to be recorded. Since the width of the object to be recorded can vary greatly, depending on the application, and since increasingly smaller structures are required to be detected, special high-resolution sensors have been employed in prior art devices, which high powered sensors entail substantial purchasing costs.
DE 40 24 618 A1 discloses a device for detecting surface information by the use of several sensors, each of which has a lens arrangement assigned to it. The surface information is supplied to these lens arrangements by beam splitting devices.
DE 33 38 168 A1 shows a sensor with several pixels, which pixels can be selectively switched on.
JP 63-240 261 A shows two line sensors, to each of which an optical device is assigned and whose image areas overlap. These overlapped areas are memorized and are selectively read out from the memory.
U.S. Pat. No. 4,009,388 discloses an image sensor having several individual sensors, each with several pixels. Each individual sensor is assigned to its own optical device.